1. Field of the Invention
This invention relates to a device and a method for detecting the position of a dimple of a disk drive suspension incorporated in, for example, a hard disk drive (HDD).
2. Description of the Related Art
A hard disk drive for writing and reading data to and from a magnetic disk includes a disk drive suspension (hereinafter simply referred to as the suspension) and a magnetic head disposed on the distal end portion of the suspension. The suspension is mounted on an actuator arm of a carriage. The suspension is provided with a base plate, load beam, flexure, etc. The flexure is fixed on the load beam. A gimbal portion including a tongue portion is formed on a part of the flexure. A slider that constitutes the magnetic head is mounted on the tongue portion.
A dimple is formed on the distal end portion of the load beam by stamping. The dimple projects substantially in a hemisphere toward the tongue portion of the flexure, and its top is in contact with the tongue portion. The reverse surface of the dimple is concave. The slider fixed on the tongue portion swings in a rolling or pitching direction around the dimple top. It is necessary, therefore, to accurately ascertain the position of the dimple (especially, the dimple top).
A device for measuring the respective positions of components of the suspension is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2006-308425 (Patent Document 1). Once the flexure is fixed to the load beam, in a manufacturing process for the suspension, the dimple is located on the reverse side of the tongue portion. Thus, the detection device described in Patent Document 1 cannot optically detect the position of the dimple top.
Even though the flexure is fixed to the load beam, the reverse side (concave surface) of the dimple can be optically observed without being hindered by the flexure. Thereupon, the inventors hereof hit upon an idea to detect the dimple position by irradiating the dimple with illumination light from behind it. Specifically, light reflected by the reverse surface of the dimple is imaged, and image processing is performed for binarization. Then, the position of the dimple top is obtained based on a light spot region obtained by the binarization.
If the shape of the dimple is distorted or if the dimple surface is rough, however, a light spot region (on-region) above a binarization level cannot be obtained, in some cases. If the reflected light is weak, therefore, dimmer control is performed such that the illumination light is intensified to intensify the reflected light in order to obtain a light spot region above the binarization level.
However, investigation by the inventors hereof revealed that the position of the dimple top cannot be accurately detected, depending on the conditions of the dimple, if the dimple position is obtained based on the dimmer control. If the dimple shape is distorted, in particular, a detected position (apparent position) of the dimple top may be considerably deviated from an actual dimple top position, in some cases. The reason for this will be described below.
The dimple is formed by striking and plastically deforming a part of the load beam by means of a precision press tool. As the pressing frequency increases, therefore, the tool may be worn or deformed, or its molding surface may be roughened. Thereupon, the dimple shape or surface may become irregular or rough.
Ideally, the dimple has the dome shape of a circular-arc rotor (substantially hemispherical) such that its top is located on its center. In this case, the illumination light directed toward the reverse surface of the dimple from the reverse side thereof is reflected by the reverse side of the dimple top and directed straight to an imaging element. Thus, a peak of the reflected light appears in a position corresponding to the dimple center, as indicated by reflected light distribution A typically shown in FIG. 9, for example. If this reflected light is weak, reflected light distribution A may sometimes fail to exceed a binarization level SH1. In such a case, reflected light distribution B above the binarization level SH1 can be obtained by intensifying the illumination light, and hence, the reflected light.
The “dimple center” as stated herein implies the center of a circular contour of the dimple, as viewed from above the load beam. On the other hand, the “dimple top” is that part of the obverse surface (convex surface) of the dimple which projects farthest toward the tongue portion. If the dimple is distorted, the dimple top may be deviated from the dimple center, in some cases.
If the dimple top is deviated from the dimple center, a peak of the reflected light appears in a position off the dimple center, as indicated by reflected light distribution A′ typically shown in FIG. 10, for example, and distribution A′ is bilaterally asymmetrical. If reflected light distribution A′ is below the binarization level SH1, reflected light distribution B′ above the binarization level SH1 can be obtained by intensifying the illumination light. If the illumination light is intensified, however, a peak of reflected light distribution B′ is inevitably further deviated from the dimple center, as indicated by arrow D in FIG. 10. Therefore, an apparent position of the dimple top obtained based on this light spot region is deviated from the actual dimple top position by ΔC. Thus, the top position cannot be accurately detected, depending on the conditions of the dimple.